1. Field
This invention relates to green-colored, wet-process phosphoric acid suitable for ammoniation into liquid fertilizer and to processes for producing same.
2. State of the Art
Various techniques and the desirability of producing a green-colored, wet-process phosphoric acid are described in U.S. Pat. No. 4,808,391 to Leavitt. The problems of processes prior to Leavitt are discussed therein with reference to carbon elimination and the minimization of sludge formation in the ammoniated product. Leavitt described a two-step oxidation/reduction process to produce an acceptable green-colored, liquid wet-process phosphoric acid suitable for ammoniation into a green-colored liquid fertilizer. Such green-colored ammonium phosphate liquid fertilizer had become the standard in the industry prior to utilization of wet-processes. Prior process has used calciners to minimize carbon and produce a processed ore suitable for dissolution and production of green-colored phosphoric acid.
The green color of the phosphoric acid is generally postulated to be due to certain incidental metal impurities which exist as chromophores as a result of the oxidation of the wet-process phosphoric acid. When ammoniated, the green-colored phosphoric acid produced a green colored liquid fertilizer which had become the acceptable standard in the industry.
Leavitt indicates that a one-step process described by Moore in Canadian Pat. 955,033 did not produce a wet-process acid with a desirable green color.